1. Technical Field
This invention relates to machine finishing tools for performing chipless finishing processes and, more particularly, to a roller burnishing tool for burnishing simultaneously the inner and outer surfaces of an annular metal workpiece and effecting a stress reversal of the material of such a workpiece.
2. Discussion
Chipless finishing tools are used in a wide variety of machine tool applications and processes to cold work metal surfaces to produce a very uniform, dense, low micro surface finish. A principal advantage of chipless finishing is the ability to produce such finishes without removing metal chips from the workpiece, which would otherwise occur in most other finishing processes such as reaming, boring and grinding.
One particular chipless finishing process is generally known as roller burnishing. In roller burnishing, metal is cold worked under a high force. The high force is designed to exceed the yield strength of the metal being finished, thereby causing a plastic deformation of its surface material. The deformation causes the peaks on the surface being finished to flow into valleys on the surface, thereby effecting an extremely smooth surface.
Roller burnishing tools generally are available for finishing a wide variety of surfaces including the outer diameter of cylinders and inner diameters of circular holes. With an inner diameter burnishing tool the high force needed for causing the necessary surface deformation is generated by a number of independent, tapered "rolls" housed within a "cage". Disposed within the cage is an inversely tapered mandrel which bears upon the rolls and, when rotated, causes the rolls to rotate and thereby apply a high, steady, rolling pressure against the inner surface of the workpiece. With an outer diameter roller burnishing tool, the mandrel circumscribes the rollers and forces them inwardly against an outer surface of a workpiece inserted within the rollers. As the mandrel rotates it causes the rollers to rotate and apply a steady rolling pressure against the outer surface of the work surface.
A particularly useful process performed by rollers is "stress reversal" of the material of a workpiece. Typically this is effected by feeding a piece of material through a plurality of parallel rollers. The rollers are further arranged so that the material moving between them is overbent in successively diminishing amounts, thereby removing, for example, the "curl" in a section of formerly coiled sheet metal.
Although stress reversal tools such as was just described above operate well in a flat plane, it would be advantageous if such a stress reversal operation could be performed on an annular workpiece. Performing a stress reversal operation on a distorted annular workpiece would help to remove the deformation and cause a more nearly perfect cylindrical surface to be formed.
It is therefore a principal object of the present invention to provide a roller burnishing tool operable to roller burnish simultaneously the inner and outer surfaces of an annular workpiece.
It is a further object of the present invention to provide a roller burnishing tool operable to enable successive cycles of diminishing stress reversal to be effected upon an annular workpiece.
It is still a further object of the present invention to provide a burnishing tool capable of performing, simultaneously, burnishing and stress reversal operations on an annular workpiece.
It is another object of the present invention to provide a roller burnishing tool operable to remove distortions and to cause a thin workpiece to become more nearly cylindrical.